1. Field of the Invention
This invention relates to a pattern data generator which is employed in an apparatus for producing a disc-like recording medium for forming pre-formatted data patterns such as servo information, clock information and read-only information in a magneto-optical disc or a magnetic disc having a step between a recording region and a non-recording region thereof, and which is adopted particularly for supplying pattern data in accordance with the pre-formatted data to an optical recording device such as a laser cutting device for scratching the pre-formatted data pattern on a base plate for the disc using a lithography technique.
2. Description of the Related Art
In general, a magneto-optical disc and a magnetic disc of the conventional sample servo format are both provided with a data area 101 in which information signals are recorded and a servo area 102 in which servo information is recorded in advance, as shown in FIGS. 1 and 2. In the servo area 102, so-called pre-formatted data are formed such as servo marks 103, clock marks 104, and access codes and read-only information (ROM information) 105.
For recording the pre-formatted data in the magneto-optical disc, disc substrate 110 is provided with pits corresponding to the pre-formatted data when it is molded, and a reflecting film or a vertical magnetization film (recording film) 111 is formed thereon, as shown in FIG. 3. Thus, viewed from the side of the disc substrate 110, substantially circular lands are formed, that is, the servo marks and the clock marks.
As for recording of the pre-formatted data in the magnetic disc, there are two methods. By one method, the disc substrate is provided with pits corresponding to the pre-formatted data when it is molded, similarly to the above and as shown in FIG. 4A. After a magnetic film 112 is formed on the disc substrate 110, pits and lands in the servo area are magnetized in different directions. Thus, the magnetized information is formed as the servo marks and the clock marks.
By the other method, the magnetic film 112 is formed on the entire flat surface of the disc substrate 110, as shown in FIG. 4B. After a portion of the magnetic film 112 corresponding to the pre-formatted data is partly removed using a known lithography technique, the magnetic film in the servo area is magnetized. Thus, the residual portions of the magnetic film or the removed portions are formed as the servo marks and the clock marks.
Conventionally, a laser cutting device is used for forming the pre-formatted data pattern.
After a photoresist film is formed on a circular substrate as the base for the disc, a resist latent image in accordance with the pre-formatted data pattern is formed by the laser cutting device. After that, the photoresist film is developed. Thus, a portion of the photoresist film corresponding to the pre-formatted data pattern is removed, and a metallic film is vapor-deposited on the entire surface including the residual photoresist film, to produce a metallic base plate. Then, a mother and a stamper are duplicated from the metallic base plate, so as to mold the disc substrate 110 of synthetic resin from the stamper. At the same time, pits are formed in portions corresponding to the pre-formatted data pattern.
By forming the recording film on the surface of the disc substrate 110 having the pits formed thereon, the magneto-optical disc is completed. On the other hand, by forming the magnetic film 112 on the surface of the disc substrate 110 having the pits formed thereon, and then magnetizing the pits and lands in different magnetization directions, the magnetic disc is completed.
The pattern data as the base for forming the pre-formatted data pattern on the circular substrate is generated by the pattern data generator which is connected to a preceding stage of the laser cutting device.
The conventional pattern data generator is comprised of combination of a counter and a decoder, as shown in FIG. 5. The circuit shown in FIG. 5 is constituted by including a rotary encoder which is mounted to a motor for rotating in one direction a rotation table for fixing the base plate and in which B units of pulses are generated for each rotation of the rotation table, a PLL 121 for multiplying an encoder pulse St supplied from the rotary encoder by A, an N-ary counter 122 for sequentially outputting as N-ary data a value of counted pulses St supplied from the PLL 121, a decoder array 123 constituted by a plurality of arrayed decoders 123a, 123b, 123c, . . . for outputting a detection signal when a peculiar value is produced among the values output from the N-ary counter 122, and an OR circuit 124 to which outputs from the respective decoders constituting the decoder array 123 are supplied and which calculates OR of these outputs.
A technique of supplying the format data from the pattern data generator to the laser cutting device is described. First, the rotation table with the circular substrate fixed thereon is rotated at a constant rotation rate. Along with this rotation, the encoder pulse is sequentially output from the rotary encoder. The encoder pulse St is multiplied by A in the PLL 121 on the subsequent stage, and is supplied to the N-ary counter 122. The N-ary counter 122 sequentially outputs as the N-ary data the value produced by counting the number of pulses Sc sequentially supplied from the PLL 121.
The decoders 123a, 123b, 123c, . . . of the decoder array 123 detect the corresponding peculiar values among the N-ary data supplied from the N-ary counter 122, and output detection signals to the OR circuit 124 on the subsequent stage. For example, if data "00000001" is output from the N-ary counter 122, a detection signal "1" is output from the first decoder 123a. If data "00001010" is output from the N-ary counter 122, a detection signal "1" is output from the second decoder 123b. If data "00010000" is output from the N-ary counter 122, a detection signal "1" is output from the third decoder 123c. The detection signals from the respective decoders 123a, 123b, 123c, . . . are to be supplied to the OR circuit 124 on the subsequent stage, and be supplied to the laser cutting device as data in series, that is, the format data.
Then, the format data which is generated by the pattern data generator is laser-scratched as a pattern onto the circular substrate while a cutting head, constituted by for example an objective lens, of the laser cutting device is transmitted in a radial direction of the circular substrate at an equal rate per rotation of the substrate. Thus, a cyclic pattern which is repeated for every N clocks (N=A.multidot.B/n, with n being an integer) and which is arrayed in a circumferential direction and a radial direction is laser-scratched on the photoresist film on the circular substrate.
In the conventional pattern data generator, it is difficult to generate pattern data other than the cyclic pattern data which is repeated for each N clocks, and it is impossible to output a mixture of pattern data of high frequency of occurrence, such as data which are the same in each segment, e.g. servo marks and clock marks, and pattern data of low frequency of occurrence, such as a segment address and ROM information in accordance with the segment.
Modification of the pattern data in accordance with the changes in use thereof, such as modification of the pattern data for the magneto-optical disc to the pattern data for magnetic disc, cannot be realized only with a simple changeover of the connecting order of the decoders. Instead, it is necessary to modify the decoders themselves in accordance with the change in use, or to use other decoders. In addition, it is necessary to take account of the N-ary data output from the N-ary counter and decoding characteristics (i.e., at which value for the decoder to output the detection signal) of all the decoders to be built. Thus, a very troublesome operation as described above is needed.
Recently, it is requested that, as a head positioning driving system for carrying out recording in/reproduction from the disc, a linear positioning driving system which shifts in the radial direction of the disc be switched to a rotating positioning driving system which rotates around one supporting point. This is based on the fact that the rotating positioning driving system is more resistant to external disturbance than the linear positioning driving system and exhibits higher positioning accuracy.
In the rotating positioning driving system, the locus of shift of the head draws an arc. In the conventional pattern data generator, only the cyclic pattern data which are repeated for each N blocks can be generated, as described above. For example, in case the generated pattern data are formed in the circular substrate as the format data pattern, base points thereof such as clock marks are radially and linearly arrayed all the time, as shown in FIG. 6. In the rotating positioning driving system, as seen from the locus of shift of the head thereof, it is necessary for the positions of the base points or the clock marks of the format data pattern to draw an arc along the locus of shift with respect to the radial direction of the circular substrate or the disc.